1. Field of the Invention
The present invention relates to fastening nuts, such as nuts for fastening grinding wheels to the spindles of portable grinders. In particular, the present invention relates to fastening nuts with loosening assist functions for facilitating the loosening of the nuts via application to the nuts of small loosening forces.
2. Description of the Related Art
In general, a fastening nut is engaged with and fastened onto a male thread formed on a front end of a spindle in order to mount a disk-like grinding wheel to a motor-driven spindle of a portable grinder. The grinding wheel is mounted so as to not move in an axial direction or also in a rotational direction relative to the spindle. The grinding wheel can be clamped between the nut and a flange formed on the spindle so as to not move in an axial direction or in a rotational direction.
In this kind of grinder, the resistance force applied to the grinding wheel by a workpiece during a grinding operation may act to further fasten (i.e., tighten) the nut. Therefore, it is often difficult to loosen the nut in order to remove the grinding wheel from the spindle. In order to solve this problem, various measures have been proposed in the art.
For example, U.S. Pat. No. 5,175,963 (corresponding to Japanese Patent No. 2801324) teaches a fastening nut in which steel balls are provided. The steel balls maintain a state where wedge members, disposed at tri-sectional positions about a male threaded portion of a spindle, are fitted between a grinding wheel and a nut body fastened onto the male treaded portion. The steel balls can maintain the fastened condition of the nut body onto the male threaded portion. According to this type of fastening nut, rotation of an operation ring containing recesses, formed in the inner circumference of the operation ring for receiving the steel balls, allows the steel balls to move into the recesses and become displaced radially outward. Consequently, the wedge members are moved in directions for facilitating removal from positions between the nut body and the grinding wheel. Therefore, this operation enables a relatively small operational force to loosen the nut body, which has been fastened onto the male threaded portion of the spindle.
Japanese Laid-Open Utility Model publication No. 4-118972 teaches a fastening nut in which steel balls are respectively disposed between an operation ring and nut segments that correspond to tri-sectional segments of a nut about a male threaded portion of a spindle. The steel balls can be moved into recesses formed in the nut segments so as to displace the nut segments in radially outward directions. The nut segments fastened onto the male threaded portion of the spindle can then be loosened.
Throughout the specification, the term “radial direction” in relation to the movement of the nut segments is used to indicate the radial direction about an axis of a male threaded portion (or female threaded portion) to which a nut is fastened. Therefore, the term “radially outward direction” is used to indicate a direction away from the axis of the male threaded portion. The term “radially outward direction” is used to indicate a direction towards the axis of the male treaded portion.
However, in the case of the former type of fastening nut incorporating separated wedge portions, a single steel ball is engaged with and released from each of the corresponding wedge portions. Similarly, in the case of the latter type of fastening nut incorporating nut segments, a single steel ball is engaged with and released from each of the corresponding nut segments. Therefore, there exists a problem in that the positions of the wedge portions or the nut segments are liable to become unstable, particularly when the nut is fastened.